1. Field of the Invention
The present invention relates to manufacturing of a semiconductor device, and more particularly, forming of a thin film such as a dielectric film in a capacitor.
2. Description of the Related Art
The capacitance (C) of a capacitor is proportional to the area (A) of the capacitor""s electrodes and a dielectric constant (xcex5) of a dielectric material between the electrodes, and inversely proportional to distance (d) between the electrodes, as shown in the following equation.
C xcex1xcex5(A/d)
Thus, increasing the area (A) of electrodes, using a dielectric film having a high dielectric constant, or decreasing the distance between the electrodes can increase the capacitance (C) of the capacitor.
As semiconductor devices become more highly integrated, the areas available for capacitor formation within semiconductor devices become smaller. Accordingly, techniques have been developed for increasing the capacitance of capacitors formed in small areas. One technique uses three-dimensional electrodes to increase the area (A) of the electrodes, but the three-dimensional electrodes are subject to structural restrictions. Use of a dielectric film having a high dielectric constant (xcex5) can increase the capacitance (C) of a capacitor and permit high semiconductor integration. In addition, a thinner dielectric film reduces the distance (d) between electrodes and produces higher capacitance of a capacitor, but reducing the distance (d) between the electrodes often has the drawback of increasing the leakage current of the capacitor.
Recently, tantalum oxides, such as a tantalum pentoxide (Ta2O5) having a high dielectric constant (xcex5), have been tried as dielectric films for capacitors. However, with a tantalum pentoxide film, leakage current can be large when the film is thin. A problem with tantalum pentoxide is non-uniform film deposition, and oxygen and carbon impurities often allow the leakage current through weak portions of the tantalum pentoxide film. To solve the leakage problem, several methods have been suggested. Among the suggested methods is a dry-oxygen (dry-O2) annealing, and a low temperature ultraviolet-ozone (UV-O3) annealing at 500xc2x0 C. or less followed by a dry-oxygen annealing, IEEE Transactions on Electron Devices, Vol. 38, No. 3, March 1991, entitled xe2x80x9cUV-O3 and Dry-O2; Two-Step Annealed Chemical Vapor Deposited Ta2O5 Films for Storage Dielectrics of 64-MB DRAM""sxe2x80x9d, by Shinriki and Masayuki Nakata, which is hereby incorporated by reference in its entirety, discloses the latter method. In the known methods, formation and UV-O3 annealing of the tantalum oxide film are respectively performed in separate chambers shown in FIGS. 1 and 2.
Referring to FIG. 1, a chamber 8 for forming a tantalum oxide film includes a shower head 10 in an upper portion of chamber 8. Shower head 10 receives pentaethoxytantalum as a source gas for the tantalum oxide film from a supply line 12 and oxygen (O2) as a reaction gas from a second gas supply line 14. A first valve 12a and a second valve 14a are in the first and second gas supply lines 12 and 14, respectively. A susceptor 16 is on the floor of the chamber 8 for mounting of a wafer 18. A pumping line 20 connects to the bottom of the chamber 8, and a pump 22 attaches to the pumping line 20. After forming the tantalum oxide film, wafer 18 becomes a wafer 23, which is transferred to an annealing chamber 9 (FIG. 2). In annealing chamber 9, a UV-O3 annealing is performed on the tantalum oxide film.
Referring to FIG. 2, UV-O annealing chamber 9 includes a quartz window 11 on the ceiling thereof. A UV lamp housing 13 includes a UV lamp 15 for generating UV rays that pass through quartz window 11 into chamber 9. A shower head 17 below quartz window 11 is also made of quartz to uniformly pass UV rays into chamber 9. Shower head 17 supplies a gas mixture containing oxygen (O2) and ozone (O3) gases that form an oxide film with a uniform thickness. Shower head 17 connects to an ozonizer 19 installed outside chamber 9. A susceptor 21 is on the floor of chamber 9 and below shower head 17, and wafer 23 having the tantalum oxide film is on susceptor 21. An ozone decomposer 25 connects to a bottom of chamber 9 via a pumping line 27, and a pump 29 connects to ozone decomposer 25.
As described above, the conventional method forms a tantalum oxide film and uses a separate chamber for a UV-annealing to remove defects from the tantalum oxide film.
In accordance with an embodiment of the present invention, an apparatus for forming a dielectric film on a semiconductor substrate includes a shower head on in a reaction chamber, and a mounting stand in the reaction chamber, below the shower head. The semiconductor substrate is loaded on the mounting stand. A first gas line for supplying a source gas for depositing the dielectric film and a second gas supply line for supplying a reaction gas for depositing the dielectric film and an annealing gas, typically ozone, for annealing the dielectric film connect to the shower head.
When the dielectric film is a composite dielectric film, the first gas supply line may include several lines, which supply respective source gases for the layers of the composite dielectric film. An ozonizer connects to the second gas supply line in parallel. The second gas supply line can include respective gas supply lines for supplying the reaction gas and the annealing gas.
A supply line for an inert gas such as nitrogen (N2) or argon (Ar) gas may connect to the second gas supply line for purging the reaction chamber and the second gas supply line. The inert gas supply line and the second gas supply line can respectively include mass flow controllers (MFCs). An ozone decomposer connects to the reaction chamber via a pumping line between the ozone decomposer and the bottom of the reaction chamber. A pump connects to the ozone decomposer.
The apparatus may further include a second pumping line, which bypasses the ozone decomposer, to protect the ozone decomposer from contamination caused by gas discharged during deposition of a dielectric film. The ozone decomposer connects to the ozonizer via an ozone purifying line, and a control valve on the pumping line directs the gas flow from the reaction chamber to the second pumping line or the ozone decomposer.
According to another embodiment of the present invention, a reaction chamber includes five (first through fifth) semiconductor substrate mounting stands. Each of the second through fifth semiconductor substrate mounting stands faces respective shower heads. The chamber also includes a gas spraying means capable of forming air curtains of an inert gas around the shower heads.
According to an aspect of the invention a method for forming a dielectric film includes (a) depositing a dielectric film on a semiconductor substrate, (b) annealing the dielectric film at a temperature lower than a crystallization temperature of the film, and (c) annealing the dielectric film at a temperature higher than the crystallization temperature. When a tantalum oxide dielectric film is formed, the tantalum oxide film is first annealed at approximately 450xc2x0 C. in an ozone or oxygen atmosphere and then annealed in a dry-oxygen or wet-oxygen atmosphere.
The steps (a) and (b) or the steps (a), (b), and (c) can be performed in situ in an apparatus. In particular, a reaction chamber including a shower head for source and annealing gases and a susceptor for heating the semiconductor substrate can perform steps (a) and (b). A first gas supply line that supplies a source gas for forming the dielectric film and a second gas supply line that supplies a reaction gas for forming the dielectric film and an annealing gas connect to the shower head. A second dielectric film may be further formed on the dielectric film and then annealed in situ in the same chamber. In the step (b), the semiconductor substrate can be annealed by a resistance heating or a lamp heating method. The source gas typically comprises a metal oxide gas corresponding to one selected from a group consisting of tantalum oxides such as pentaethoxytantalum (Ta(OC2H5)5), titanium oxides and aluminum oxides. When a tantalum oxide gas is the source gas, oxygen (O2) and ozone (O3) gases are the reaction gas and the annealing gas, respectively. In the step (a), the first gas supply line supplies the source gas, and the second gas supply line supplies the reaction gas. When there is a large difference in processing pressure between the steps (a) and (b), a turbo molecular pump (TMP) reduces the time required for adjusting the pressure between steps (a) and (b).
Steps (a) and (b) can be performed in situ in the above-described reaction chamber using five semiconductor substrate mounting stands. One such process performs steps (a) and (b) while a semiconductor substrate remains on the same mounting stand. In this case, the steps (a) and (b) include the sub-steps of: pre-heating the semiconductor substrate having the thin film on the first semiconductor substrate mounting stand; and forming and annealing the dielectric films on the pre-heated semiconductor substrate.
Steps (a) and (b) can also be performed on different semiconductor substrate mounting stands. For example, the steps (a) and (b) include the sub-steps of pre-heating a semiconductor substrate having the thin film on the first semiconductor substrate mounting stand, forming dielectric films on the semiconductor substrate while on the second and fourth stands, and annealing the dielectric films when substrates are on the third and fifth semiconductor substrate mounting stands.
Steps (a), (b), and (c) can be performed in situ in a furnace or in rapid thermal processing (RTP) equipment.
For a tantalum oxide dielectric film, step (b) may be performed at between about 500 and about 700xc2x0 C., preferably, 600xc2x0 C., in an oxygen atmosphere, and step (c) may be performed at between about 700 and about 900xc2x0 C., preferably, 800xc2x0 C., in an oxygen atmosphere.
According to another embodiment of the invention, a method for forming a dielectric film includes (a) forming a dielectric film on a semiconductor substrate and (b) annealing the dielectric film. For this method, step (b) is performed at a temperature near the crystallization temperature of the dielectric film in an ozone atmosphere, and the dielectric film can be formed of tantalum oxide at between about 500 and about 700xc2x0 C., preferably, 600xc2x0 C., in an ozone atmosphere.
According to still another embodiment of the invention, a method for forming a dielectric film includes (a) forming a dielectric film on a semiconductor substrate, (b) annealing the dielectric film at a temperature lower than the crystallization temperature of the film, and (c) second-annealing the dielectric film at a temperature higher than the crystallization temperature, wherein the steps (b) and (c) are performed in situ in the same apparatus.
In the above embodiments, the material of the dielectric film is selected from the group consisting of tantalum oxide (Ta2O5), titanium oxide (TiO2), aluminum oxide (Al2O3), yttrium oxide, vanadium oxide and niobium oxide.
As described above, embodiments of the present invention share one gas supply for both forming and annealing of a thin dielectric film, and forming and annealing of the thin film are performed in situ in a chamber having the shared gas supply. Accordingly, the present invention can reduce the processing time of the thin film, thereby improving the productivity of a semiconductor device manufacturing process. In addition, inflow of impurities into the thin film is reduced, and equipment for forming and annealing of the thin film is simplified, reducing the amount of equipment required.